1. Field of the Invention
The present invention relates to a layer stack formation powder material, a powder layer stack formation hardening liquid, a layer stack formation material set, and a layer stack object formation method.
2. Description of the Related Art
Conventionally, artificial bones have been produced from metallic materials such as stainless and a titanium alloy, wear-resistant plastics, etc., and used for bone replacement. Such artificial bones act in place of dysfunctional joints, but problematically cannot endure a long time of use, because metallic materials and wear-resistant plastics incur aging changes such as wear, corrosion, and swell. Ceramics based on calcium phosphate can be raised as a material to replace them. Currently known ceramics include those for providing scaffolding for bone formation, and those that promote formation of new bones while themselves being absorbed into the bones along with time, and transform to bones in the future.
As bone prosthetic materials for providing scaffolding for bone formation, for example, materials such as hydroxyapatite that have excellent affinity with bone tissues and directly attach to bone tissues without a mediating material are often used. With implantation of such a bone prosthetic material into a bone defect portion, bone repair advances swiftly based on the scaffolding of the bone prosthetic material. However, hydroxyapatite cannot transform to bones by itself, and there is a risk that residual hydroxyapatite may cause troubles in the living bodies. On the other hand, any bone prosthetic material that can transform to bones can, when implanted in bone tissues, promote the osteogenic action of the bone tissues and advance bone repair easily and more swiftly.
For example, tricalcium phosphate is known as such a material that can transform to bones. The degree of how tricalcium phosphate is absorbed into bone tissues is dependent on the shape and texture of an object made of tricalcium phosphate. That is, a porous texture object has a large surface area due to its texture, can be absorbed into bone tissues easily, and also can be phagocytosed by phagocytic cells easily. In contrast, a dense texture object is absorbed extremely slowly, and cannot be phagocytosed by phagocytic cells easily. It is expected that utilizing the characteristic differences due to the texture, and combining a porous texture portion and a dense texture portion would lead to expression of a desired biocompatibility (see Japanese Patent Application Laid-Open (JP-A) No. 05-237278). However, none of such combination materials have strength of a level applicable as a thighbone that receives a heavy load. Further, not only does it take a long time to form such materials into a desired shape, but it is impossible to make them into a fine shape including an internal structure, particularly in the case where this process is by cutting.
Techniques of forming real three-dimensional objects based on three-dimensional shape data generated by 3D CAD or the like are generically called rapid prototyping techniques. According to an object formation method using a highly heat-resistant powder as a material among such rapid prototyping techniques, it is possible to produce a mold or a core cylinder without using a model or a wooden pattern, which makes it possible to realize an extremely fast foundry production process.
This rapid prototyping technique is also called layer stack formation method, and stacks up cross-sectional shapes of an object as layers, and forms a three-dimensional object. Furthermore, there are proposed various layer stacking methods that are one type of the rapid prototyping techniques, and use a powder as a material (powder adherence methods) (see, e.g., U.S. Pat. Nos. 5,204,055, 5,902,441, 6,375,874, JP-A No. 09-324203, and JP-A No. 2004-42546).
For example, there is proposed a technique for “an artificial bone forming method by powder lamination method”, wherein the technique forms a powder bone material that hardens by hydration into a powder layer, to thereby form an artificial bone having a greater strength (see Japanese Patent (JP-B) No. 4575295). However, it is difficult to obtain a sufficient strength based on hardening by hydration proposed, and in particular, it is difficult to apply such a material at a portion that receives a load, such as a thighbone.
This powder lamination object formation method is advantageous for fine shaping mentioned above. However, calcium phosphate reactive with water as used in JP-B No. 4575295 tends to transform to unabsorbable hydroxyapatite by being transplanted into a living body. In this case, the transplanted material may remain in the body for a long term and cause troubles as described above.
Hence, it is preferable that the transplanted material be not left transformed to a crystal in the body, but be left there in a state of having potential to transform to a bone eventually. Further, for powder layer stack formation by ink jetting, it is preferable that the powder harden as soon as possible after a hardening liquid lands on the powder. Hence, it is requested to provide a hardening liquid for powder layer stack formation that can impart a bone transformation ability to the powder, can harden the powder quickly, and can form a layer stack object having a complex three-dimensional shape with a high strength and a good precision.
Calcium phosphate transplanted into a living body may not transform to a bone at a satisfactory speed, or an artificial bone implanted by a medical operation may require a considerable time before it is high time to remove an external fixator. When bone regeneration is slow, it is feared that a soft tissue may wander into the bone defect portion and inhibit bone regeneration. To promote bone regeneration, it is proposed to add a bonemaking protein such as BMP. However, even when an object made of calcium phosphate containing a bonemaking protein is formed by ink jetting, the protein will be deactivated and become ineffective if the object is burned afterwards. Hence, for object formation by ink jetting, it is preferable that a bonemaking protein be added after burning, or that bone regeneration be realized with an inorganic material that will not become ineffective even when burned. Examples of such an inorganic material include minerals such as silicon and zinc.